This invention relates generally to circuit testing devices, and more particularly concerns apparatus to test for presence of voltage, and also for voltage level and electrical continuity. The invention enables the use of a single tester probe to test for presence of voltage and voltage level, and two tester probes to test for continuity, no switching devices being required and with the further advantage that no damage or injury can occur to the device or the user. The presence of 120, 220, and 440 volts as in homes, and 12, 18 and 24 volts as in autos and other devices can be determined using a single probe, with sound or light indicators being activated, the use of a neutral or ground not being required.
There is need for circuitry to quickly locate a defective engine spark plug, especially when the engine is not running. Further, as regards homes, electrical contractors and electricians must frequently determine whether or not voltage is present at a terminal, lead or line, as for example 120, 240, or 480 volts. If the outlet or terminal being tested is difficult to reach, the running of a separate ground line to accomplish the test becomes very difficult. Such workmen also frequently need to know if there is electrical continuity beteen two terminals; for example, if such continuity is lacking as between neutral and ground terminals at a receptable, there is the possibility of a break in the netural wire. Prior devices for resolving these questions have lacked the many unusual advantages in construction, mode of operation and results as are provided by the present invention.